Thermostatic control



Aug. 24, w43 FQ.v J. DOUGHERTY THERMOSTATIC CONTROL Filed May 18, 1942' 2 Sheets-Sheet l Aug. 24, w43.

R. J. DOUGHERTY 2,327,582

THERMOSTATIC CONTROL Filed May 18, 1942 2 Sheets-Sheet 2 H5. zl/

atented Aug. '24, i943 iJ-Nlrlazn STATES PATENT OFFICE THERMOSTATIC CONTROL Robert J. Dougherty, Ambler, Pa., assigner to Application May 18, 1942, Serial No. 443,360

4 Claims.

My invention relates to devices for controlling the supply of gas to the burner of an automatic gas-fired water heater, wherein the burner is provided with a pilot which normally remains lighted continually during the operation of the heater, regardless of Whether the burner is on or foi It is customary to control the temperature of the water in such heaters by a suitable thermostat, located in the water compartment, which eects an automatic shutting ofi of the supply of gas to the main burner when the water in the heater reaches a predetermined temperature. The action of the thermostatic control also restores a flow of gas to the main burner when the temperature of the water in the water compartment falls below the temperature for which the thermostat is set.

It is also usual practice to include in such water heaters a safety shut-off device to automatically shut off the main gas supply to the burner should the pilot become extinguished for any cause.

Accordingly, in heaters of the prior art, two sets of valves and valve casings ordinarily have been providedfthe operation of one of which is eiected by the thermostat located in the Water compartment, and the operation of the other is eiected by the safety shut-off device. In order that these valves be operated safely, it is essential that both of them be absolutely tight when closed and that each be designed for a maximum of opening when in open position. Furthermore, it is essential that the gas passages be of such dimension that a minimum drop in pressure of the gas results. Pressure drop may result from constricted passageways or such changes in direction of the gas which causes turbulence, or an eddying effect.

Although some prior art structures have utilized a single casing for both the thermostat and safety shut-off, in all such structures separate valves are used for the performing of each function.

'I'he principal feature of my invention is the combining ofthe prior art separate thermostat and safety shut-oi devices in a single device in which only one valve and body-are required to perform the dual functions which heretofore necessitated the use of two separate sets of valves, etc.

vAnother feature of my invention is to provide a device in which there is a. material reduction of pressure drop, which inherently exists when two separate valves and parts are used.

Another feature of my invention is the providing of a device in which valve adjustment is minimized because but one valve is used.

Another feature of my invention is the providing of a device which may be readily and facilely adapted to be tight when closed.

Another feature of my invention is the providing of a device in which the total number of parts and the cost thereof is materially reduced. f

Another feature of my invention is the providing of a device which is less liable to stick than an ordinary shut-off valve by reason 0f the fact that in my device the valve is constantly operating, whereas the safety shut-oi valve of the prior art closes only in an emergency.

Another feature of my invention is that its use permits the appearance of the assembled water heater to be enhanced by reason of the fact that fewer accessories are visible on the outside of the heater casing than when the multiplicity of prior art devices required to perform the same functions are used.

My invention includes the various novel features of construction, arrangement, and method of operation hereinafter moredenitely specified.

Fig. I is a fragmentary vertical sectional view of an automatic gas water heater embodying my invention. In Fig. I the thermostatic elements are shown in the position which they assume when the pilot is lighted, the main thermostat in o" position, and the valve controlling the main gas supply to the burner closed.

Fig. II is a fragmentary view of the structure shown in Fig. I, but in which the elements are shown in a position in which the pilot is lighted. the main thermostat in on. position, and the gas Valve open.

Fig. III is a view similar to Fig. lI, but in which the elements are shown in the position which they assume when the pilot is extinguished, the main thermostat in on position, and the gas valve in closed position.

Fig. IV is a fragmentary vertical sectional view of an automatic gas water heater embodying a modified form of my invention, and in which the thermostatic elements are shown in the position which they assume when the pilot is lighted, the main thermostat in on position, and the gas valve closed.

Fig. V is a fragmentary sectional view'of the structure shown in Fig. 1v, but in which the e1ements are shown in the positions which they assume when the pilot burner is lighted, the main burner is in on position, and the gas valve open.

Fig. VI is a fragmentary vertical sectional view of another modification of the devices shown in Figs. I to Ill and Figs. IV and V, and with the thermostatic elements thereof shown in the position which they assume when the pilot is lighted, the main thermostat in on position, and the gas valve open.

Referring to Fig.'l; I have shown a fragment of an automatic water heater in which my invention is embodied, including the cylindrical shell I of the water compartment which is provided with a bottom closure 2. The bottom closure 2 separates the Water compartment I from the combustion chamber 3 in which is located the main gas burner 4 of a conventional type, the right hand 'end only of which is shown in Fig. I. Gas is supplied to the burner 4 through the pipe 6, connected to a suitable source of gas supply. l have ound it desirable to include in the gas line the gas valve 1 by which the gas supply to the burner may be shut oil manually when it is desired to permanently shut off the heater. Said valve 1 has the gas passageway 8 therethrough undef control of the valve plug 9 which is provided with the opening I therethrough. In the position shown in Fig. I, said valve 1 is in open position.

Referring to Figs. I, II, and III; the valve casing I2 has the screw threaded opening I3 for engagement with tl@ screw threaded end I4 of the valve 1. Said valve casing I2 has the gas inlet I5 and outlet I6 upon opposite sides of the partition I1. Said partition I1 has valve ports I8 through it, controlled by the valve 20 which has an inner stem 2l mounted to reciprocate in the bearing 22 formed in said partition I1. Said valve 20 is continually pressed toward its valve seat 24 by a light spring 25 which bears at its inner end upon the valve 20 and abuts at its outer end against the closure cap 26 which is detachably engaged With said casing I2 in any convenient manner.

Said stem 2I is provided at its inner end, in screw threaded relation therewith, with the axial adjusting screw 21 to facilitate axial adjustment of said screw in cooperative relation with the resilient tripod spring 30 of the clicker 3I by which said valve 20 is snapped open in opposition to the pressure of the spring 25, as hereinafter described. Said clicker 3I is of the Well known type used in thermostatically operative valves, for example, the thermostatically operative valve disclosed in Letters Patent No. 1,974,646 granted to me September 25,1934. The spring 30 is made of concavo-convex form with its convex surface normally presented toward the circular thrust disk 32 which is positioned in the annular offset recess 34 formed inthe casing I2.

Said casing I2 has the cover element 36' which is detachably rigidly connected to said casing. Said cover element 36 is provided with a conical recess 31 in which the conical thrust block 38 is positioned with freedom of movement, and the base of the cone is in sliding engagement with the top surface of the clicker element 3|. The top closure 36 is provided with a screw threaded opening 40 in which is engaged a screw threaded nut 4I carrying the thermostatic element 42. The thermostatic element 42 is conveniently of the liquid lled type comprising the tube 43 which is filled with va liquid 44 having a greater coeicient of expansion than the tube 43. The left hand end portion of said tube 43 extends into the water in the Water compartment I of the heater. The liquid 44 is maintained in filled fluid tight relation within the tube 43 by means of the Sylphon bellows 46 which is rigidly fastened only at its lower end in the annular recess 41 formed in the nut 4I. The upper free end of the bellows 46 carries the' plunger 50, the lower end of which is mounted with freedom of reciprocatory movement in the bearing 5I formed in the cover 36. The lower end of the plunger 50 is adapted for engagement with the cone block 38 to effect movement of the snap spring 30 and valve 20, as hereinafter described.

sansa The outlet I6 of the valve casing I2 has the screw threaded opening i'or engagement with the screw threaded end 56 of the needle valve fitting 51 which is in engagement with the right hand mixing tube end of the main burner 4. Said fitting 51 is provided with the gas passageway 58 which affords communication between the valve casing outlet I6 and the main burner 4.

The burner 4 is provided with the orice 60 under control of the manually adjustable needle valve 6I. The right hand end of the needle valve 6I is in screw threaded engagement with a screw threaded opening 62 formed in the tting. 51. I have found it convenient to lprovide the screw threaded end of said needle valve 6I with the screw driver slot 63 to facilitate adjustment of said valve. I also have found it desirable to protect the needle valve 6I from accidental displacement by providing the screw plug 64 for closure of the screw threaded opening 52.

The safety shut-off device includes the thermostatic couple comprising the outer tube 65 formed from material which is expansionable under the influence of heat from the pilot. The right hand end of said tube 65 'is conveniently in screw threaded engagement with the screw 'threaded opening 66 formed in the cover 36 of the valve casing I2. The other element .of the thermostatic couple is the inner rod 61 which is formed from material having a negligible coeicient of expansion. The left hand end of said non-expansionable rod 61 is rigidly mounted in the plug 68 which is in integral relation with the left hand end of the tube 65. The right hand end portion of said rod 61 is mounted with freedom of reciprocatory movement in the bearing 69 formed in the valve casing cover 36. The right hand end `of said rod 61 is adapted for engagement with the cone block 38 to effect movement thereof, as hereinafter described.

Heat is normally applied to the left hand end of the tube 65 of the shutoff device by -means of the flame from the lighted pilot burner 10, which is positioned beneath the tube 65 and also so positioned with respect to the main burner 4 as to cause said main burner 4 to become lighted when gas flows thereto. The pilot burner includes the gas tube 1I Which is conveniently in screw threadedengagement with the fitting 12 in communication. with the gas supply line at some point in the gas line in which the supply of gas thereto would not be affected by the manually operative shut-off valve 1. As shown in Fig. I, I have found it convenient to connect said fitting 12 in communication with the upper end of the gas passageway 8 of the valve fitting 1. Said fitting 12 is provided with the manually operative valve 13 by which the gas supply to the pilot may be shutoff whenit is desired to shut down the heater permanently and place it in inoperative condition.

Figs. IV and V show a modified form of my invention in which a system of levers is utilized to eect movement of the clicker element which controls the operation of the valve.

Referring to Fig. IV, I have shown a fragment of an automatic water heater in which my modied form of invention is embodied, including the cylindrical shell IOI prov.ded with the bottom closure |02. The bottom closure 102 separates the compartment IOI from the combustion chamber I03.in which is located the main gas burner |04 of a conventional type, only the right hand end of which is shown in Fig. IV. Gas is supplied to the burner |04 through the pipe |06 connected to a suitable source of supply. I have found it desirable to include in the gas line the gas valve |01, similar to the gas valve 1, which is provided with the gas passageway |08 and valve plug |09 with the opening ||0 therethrough. The valve |01 is shown in open position in Fig. IV.

Referring to Figs. IV and V, the valve casing ||,2, similar to the casing `|2 shown in Figs. I, II and III, has the screw threaded opening ||3 for engagement with the screw threaded opening ||4 of the valve |01. Said casing ||2 has the gas inlet H5 and outlet ||6 upon opposite sides of the partition I1. Said partition I I1 has valve ports ||8 through it, controlled by the valve |20 which has an inner stem |2| mounted to reciprocate in the bearing |22 formed in said partition ||1. Said valve |20 is continually pressed toward its valve seat |24 by the light spring |25 which bears at its inner end against the valve |20 and abuts at its outer end against theI closure cap |26 which is detachably engaged with said casing ||2 in any convenient manner.

Said stem |2| is provided at its inner end with the axial adjusting screw |21 to facilitate axial adjustment of said screw in cooperative relation with the resilient tripod spring |30 of `the clicker |3| by which said valve |20 is snapped open in I i is detachably rigidly connected Vto said casing.

The closure |36 is provided with the screw threaded opening |40 in which is engaged thelnut |4| carrying the thermostatic element |42. The thermostatic element |42, smilar to the thermostatic element 42, comprises the tube |43 filled with a liquid |44 having a greater coeicient of expansion than the tube |43; The left hand end portion of the tube |43 extends into the water in the water compartment |0| of the heater. The liquid |44 is maintained in lled fluid tight relation within the tube ,|43 by means of the Sylphon bellows |46 rigidly fastened at its right hand end in the annular recess |41 formed in the nut |4I. The left free end of the bellows |46 carries the plunger |50, the right hand endv of which is mounted with freedom of reciprocatory movement in the bearing |5| formed in the cover |36.

The outlet ||6 of the valve casing ||2 has the screw threaded opening |55 for engagement with the screw threaded end |56 of the needle valve fitting |51 which is in engagement with the right hand mixing tube end of the main burner |04. Said fitting |51 is provided with the L-shaped gas passageway |58 which aiords communication between the outlet ||6 and the main burner |04. Said burner |04 is provided with the orifice |60 under control of the manuallyvadjustable needle valve |6|. The right hand. end of the needle valve |6| is in screw threaded engagement with a screw threaded opening |62 formed in the fitting |51. The screw threaded end of the needle valve thermostatic couple comprising the outer tube |66, the right hand end of which is conveniently in screw threaded engagement with the screw threaded opening |66 formed in the cover |36. The other element of the thermostatic couple is the inner rod |61 which is formed from material having a negligible coeicient of expansion. 'I'he left hand end of said rod |61 is rigidly mounted in the plug |68 in integral relation with the left hand end of the tube |65. The right hand end of said rod |61 is mounted with freedom of reciprocatory movement in the bearing |69 formed in the casing cover |36.

Heat is normally applied to the left hand end of the tube |65 by a flame from the lighted pilot burner |10 positioned beneath the tube |65 and also so positioned with respect to the main burner |04 as to cause said main burner |04 to become lighted when the gas flows thereto. The pilot burner includes the tube |1| conveniently in screw threaded engagement with the fitting |12 in communication with the gas supply line at some point not affected by the manually operative shut-oir valve |01. As shown in Fig. IV, the tting |12 is in communication with the upper end of the gas passageway |08 of the valve fitting |01. Said fitting |12 is provided with the manually operative valve |13.

As shown in Figs. IV and V, movement of the clicker |3| is eected by means of the levers |15 and |16 which are pivotally fulcrumed respectively at |11 and |18 upon their respective ball tipped adjustable screw studs and |8I. The studs |80 and |8| are made adjustable to facilitate the preliminary setting of the device, after which said fulcrums |11 and |18 remain xed. The screw stud |80 is conveniently adjustable by means ofthe lever |82, connected to the shank Y of the screw stud |80, which extends through the stufiing box |83, as shown in Fig. IV. The screw stud |8| is conveniently provided with the screw driver slot in alignment with the screw threaded opening |86 formed in the casing ||2. Said opening |86 is provided with the screw threaded closure plug |81.

Said levers |15 and |16 conveniently are formed as levers of the second order, and are arranged so that their respective power ends |90 and |9| may exert force upon the clicker |3|, approximately at its axis. As shown in Figs. IV and V, the power end |90 of the lever |15foverlies the power end |0| of the lever |16, and the power end |0| of the lever |16 engages the outer surface of the Clicker element |3|. The right hand end of the plunger |50 is adapted for/ engagement with the lever |15 at a point between its fulcrum and power end; and the right hand end of the rod |61 is adapted for engagement with the lever |16 at a point between its fulcrum and power end to effect movement of the snap spring |30 and valve |20, as hereinafter described.

I have shown in Fig. VI a modification of the structure shown in Figs. IV and V. In Fig. VI a single lever 215 is utilized, and its power end engages the outer surface of the clicker element 23|, similar to said clicker |3|, to effect movement of the snap spring 230 and valve 220, as hereinafter described. Said lever 215 is fulcrumed at 211 upon the ball tipped adjustable screw stud 280. -Said stud 280 is made adjustable to facilitate the preliminary setting of the device, after which said fulcrum 211 remains fixed. Said lever 215 is conveniently formed as a lever of the second order and is arranged so that its power end 290 may exert force upon the clicker 23|', approximately at its axis.

The lcasing 2|2 of the form of my invention shown in Fig, VI has the cover element 236 which is detachably rigidly connected to said casing by any convenient means. The closure 236 is provided with the screw threaded opening 240 in which is engaged a nut carrying a thermostatic element similar to the elements 42 and |42. In Fig. VI there is shown only a fragment of the plunger 250, similar to the plungers 50 and |50, the right hand end of which is mounted with freedom of reciprocatory movement in the bearing 25| formed in the cover-236.

The closure 236 is provided with the screw threaded opening 266 for engagement with the screw threaded end of the tube, similar to the tubes 65 and |65, of a thermostatic couple safety shut-off device. In Fig. VI there is shown only a fragment of the inner rod 261, the other element of the thermostatic couple, which is formed from material having a negligiblecoecient of expansion. The left hand end of said rod 261 is mounted in a plug in integral relation with the left hand end of said tube, in the same manner as is shown in Figs. I and IV. The right hand end of said rod 261 is mounted with freedom of reciprocatory movement in the bearing 269 formed in the casing cover 236. It is to be understood that a pilot, similar to the pilots and |10, is included in the form of my device shown in Fig. VI.

In the form of my invention shown in Fig. VI, the safety shut-off tube and rod 261 are mounted concentric and in a straight line with the Aclinker 23| and valve 220.

The right hand end of the plunger 250 is adapted for engagement with the lever 215 at a point between its fulcrum and power end and the right hand end of the rod 261 is adapted for engagement with the power end 290 of said lever 215 to effect movement of the snap spring 230 and valve 220, as hereinafter described.

Operation 'I'he form of my invention shown in Figs. I, II, and III operates as follows:

With the heater shut oil with both the main burner and pilot extinguished by a manual closing of the hand valve 1 and valve 13 controlling the pilot, and with the water in the water compartment cold and below the temperature for which the thermostatic element is set, the various elements within the casing I2 assume the cal thrust block 38 to exert pressure on the cone,

forcing it along the side of the conical recess 31 at A with a resultant movement of the cone in the direction of the arrow in Fig. III. Movement of the conical thrust block in the direction of the arrow in Fig. III exerts forces upon the clinker 3| which causes the tripod vspring 30 thereof to be forced against the circular thrust disk 32, thereby causing the clicker spring 30 to snap inward, or to concave position, to permit the valve 28 to be closed under the action of its light spring 25. f

lTo initiate the cycle of operation, the operator iirst opens the valve 1 which controls the gas from a suitable supply line. The operator. then opens the pilot valve 13 to the position shown in Fig, I and the pilot 10 is lighted. The heat therefrom is applied to the tube 65 which causes said tube 65 to expand and move to the left to the position in which it is shown in Fig. I. Such expansion of the tube 65 carries with it the nonexpansionable rod member 61 and causes said rod 61 to move away from the cone 33 and to the position shown in Fig. I:

With the clicker 3| relieved from pressure, it

Vmoves from the position shown in Fig. III to the position shown in Fig. II, thereby permitting the spring 30 to snap to convex position to open the valve 20, against the effective forces of its light spring 25. With the valve 20 in open position, gas flows through the pipe 6, passageway 8 in the opened Valve 1, casing inlet |5, around the valve 2U, and through the valve ports I8 to the casing outlet I6, through the passageway 58 in the fitting 51, through the burner orifice 60, and to the main burner 4 where the gas is ignited by the flame of the pilot 10 which is in close proximity to said burner 4,

As the water in the container reaches the temperature for which the water thermostat is set, the liquid 44 in the tube expands and causes the plunger 50 to move downwardly in its bearing 5| and into engagement with the conical thrust block 38 and moves said conical thrust block until it rests against the wall B of the conical recess 31. Continued pressure by the plunger 50 upon the cone 38 causes resultant movement of `said conical thrust block 38 in the direction of the arrow shown thereon in Fig, I, causing the clicker spring 30 to snap to its concave position which permits said valve 20 to be moved to closed position under the effective forces of its light spring 25, as shown in Fig. I.

When water is withdrawn from the heater to a suicient amount to cause the temperature of the water in the container to fall below that for which the thermostat is adjusted, the liquid 44 in the tube 43 cools andcontracts, thereby permitting the plunger 50 to be moved upwardly by expansion of the Sylphon bellows 46 which results in the pressure on the clicker 3| being released, thereby permitting the spring 38 to snap to convex position, and the valve again is opened and the various elements again assume the valve open position shown in Fig. II.

Should the pilot become extinguished for any reason, the tube 65 cools and contracts, thereby moving the non-expansionable rod 61 into pressure exerting engagement with the cone 38, which causes said cone to slide along the face A of the conical recess 31 and exert pressure on the clicker 3| in the direction of the arrow in Fig. III, t0 cause the spring 38 to snap to concave position and the valve 20 to be closed under the effective forces of its light spring 25. Asis well understood in the art, the forces exerted by the clicker spring when free to snap outward to convex position, are many times greater than the effective forces of the light valve spring 25.

Referring to the form of my invention shown in Figs. 1V and V; the same valve opening and valve closing effects are effected by the use of a system of levers operating on the clicker |3| and affected by the safety shut-off and water thermostat. Referring to Figs. IV and V, with the pilot lighted, the safety shut-off rod. |61 moves, in the direction of the arrow marked thereon, from the position indicated in dotted lines in Fig. IV to the position shown in full lines. Thus, when the pilot is lighted, the valve |20 is under control of the lever |15 acted upon by the plunger |50 of the water thermostat, as the lever |16 is free to oatl idly between its mechanical limits.

Assuming 'that the water inthe container |0| is below that for which the thermostat is set, the liquid |44 within the tube |43 has contracted, which has permitted the Sylphon bellows |46 to expand and move the plunger |50 to the left in Fig. V and out of pressure engagement with the lever` |15. Whenthe clicker |3| is thus relieved from pressure. it moves from the position shown in Fig. IV to the position shown in Fig. V, thereby permitting the spring |30 to snap to convex position and open the valve |20 against the effective forces of its light spring |25. With the valve |20 in open position. gas ows around the valve |20 and through the valve ports ||8` to the main burner |04 where the gas is ignited by the flame of the pilot |10. in the same manner as heretofore described with reference to the form of my invention shown in Figs. I, II, and III.

As the water in the container reaches the temperature for which the water thermostat is set, the liquid |44 in the tube |43 expands and causes the plunger |50 to move to the right, as shown in Fig. IV, in its bearing 5|. Continued pressure by the plunger |50 upon the lever |15 causes the 'power end |90 of the lever |15 to exert pressure on the clicker |3I, therebycausing the clicker spring |30 to be forced against its thrust disk |32, which causes the clicker spring |30 to snap to its concave position shown in Fig. IV, which permits said valve |20 to be moved to closed position under the effective forces of its light spring |25.

When water is withdrawn from the heater to a sufficient degree to cause the temperature of the water in the container |0| to fall below that for which the thermostat is adjusted, the liquid |44 in the tube |43 cools and contracts, thereby permitting the plunger to be moved to the left by expansion of' vthe Sylphon bellows |46 which results in the pressure on the clicker |3| beingr released, thereby permitting the spring |30 to snap to convex position, and the valve |20 again opens and the various elements again assume the valve open position shown in Fig. V.

Should the pilot become extinguished for any reason, the tube cools and contracts, thereby moving the non-expansionable rod |61 to the right into pressure exerting engagement with the lever |16 which causes said lever to exert pressure on the clicker |3| to cause the spring |30 to snap to concave position and the valve |20 to be closed under the effective forces of its light spring |25.

Referring to the form of my inventori shown in Fig. VI, the same valve opening and valve closing effects are effected by the use of but a single lever 215 operating on the clicker 23|. In the form shown in Fig. VI, the safety shut-off tube and non-expansionable rod member 2-61 are mounted concentric and in a straight line with the clicker 23| and valve 220, to thereby act directly on such parts and to eliminatel the necessity of a lever, such as the lever |16 of the form of-my invention shown in Figs. IV and V. The lever 215 bears directly against the clicker 23| and the rod 261 is positioned for engagement directly on the power end 290 of the lever 215. In the form of my invention shown in Fig'. vVI, when the'pilot is lighted expansion of the tube draws the end of the rod 261 away from the power end 290 of the lever 215, and said rod 261 thereafter does not interfere with the thermostatic action as long as the pilot remains lighted. Except for the fact that the power end 290 of the lever 215 bears directly against the clicker 23|,` the form lof my device shown in Fig. VI functions in the. same manner in response to movements of the thermostatic plunger 250 as has been heretofore described with reference to the form of my invention shown in Figs. IV and V.

It is obvious that many variations of lever arrangement are possible and, accordingly, I do not desire to limit myself to the precise details of construction, arrangement, and method of operation herein set forth', as it is obvious that various modifications may be made therein without departing from the essential features of my invention-as defined in the appended claims.

Iclaim: 1. In a thermostatically operative valve structure; the combination with thermostatic means responsive to the water temperature inlthe con- .tainer of a water heater; of safety shut-off thermostatic -means for the gas burner of said water heater; a valve casing having a gas inlet and a gas outlet with a valve port between them; a single valve responsive to both said water thermostat and said safety shut-oil thermostatic means for controlling said valve port; means for effecting snap action of said valve; and a conical block in operating relation to both of saidv thermostaticmeans and to said means for effecting snap action of said valve for transmitting movement v:from both of said thermostatic means to said means for effecting a snap action of said valve. 2. A structure as in claim 1, wherein the means for effecting snap action of said valveincludes a rigid disk and a concavo-convex snap spring element.

3. In a thermostatically operative valve structure; the combination with thermosta-tic means responsive to the water temperature in the container of a water heater; of safety shut-off thermostatic means for the gas burner of said water heater; a valve'casing having a gas inlet and a 4. A structure as in claim/3, wherein the mea-ns for effecting snap action of said valve includes a. rigid disk and a concavo-convex snap spring element.

ROBERT J. DOUGHERTY. 

